1. Field of the Invention
This invention relates to systems and methods of developing better-designed medical devices, specifically, intracorporeal medical devices and particularly cardiovascular stents and endovascular grafts.
2. Background and Description of Related Art
Atherosclerotic vascular disease is a significant health problem facing the world population today. Atherosclerosis results in two primary types of lesions—occlusive and aneurysmal, with the aorta being the primary site of aneurysmal disease. Occlusive disease is a process in which a vessel lumen becomes narrowed and the blood flow restricted. Occlusive disease is typically associated with plaque buildup on the vessel wall or a biological response to vessel injury. One approach to treatment of occlusive disease involves placing a stent inside the vessel to act as a structural scaffold and hold open the vessel, and also possibly to provide local drug delivery or local radiation treatment. Aneurysmal disease is a process in which a vessel dilates under the influence of hemodynamic pressure, and may ultimately lead to rupture of the vessel and severe internal bleeding. One approach to treatment of aneurysmal disease involves placing a TPEG (transluminally placed endovascular graft, or “stent graft”) across the aneurysm, excluding the aneurysm from hemodynamic pressure and thereby reducing or eliminating the risk of rupture. Examples of such grafts can be found in co-pending U.S. patent application Ser. No. 09/133,978, filed Aug. 14, 1998 by Chobotov, which is hereby incorporated by reference herein in its entirety.
A TPEG is an endovascular prosthetic device that lines the interior of an artery to provide flow path integrity and structural support to the damaged or diseased blood vessel. TPEGs are sometimes called “stent grafts” because they were originally created using combinations of stents and synthetic vascular graft segments. TPEGs are delivered to a blood vessel location in a compressed state, through an incision, and are then deployed at the location of concern.
The current development process of TPEGs and medical devices generally, usually involves the reiterative and sequential steps of designing, fabricating the prototype, and testing the prototype until the required performance specifications are met. Fabrication of the prototype entails the building of the actual medical device, e.g., a TPEG. Testing can involve animal testings, human clinical trials, stress, strain, and deformation testing, and the like. Stents, TPEGs and other medical devices have suffered from long development times and from design deficiencies discovered late in the development and testing process. Thus, the development of improved medical devices could be significantly accelerated if design deficiencies could be identified earlier, before committing to lengthy laboratory testing, animal studies, and human clinical trials. A system that enables early evaluation of many aspects of device performance in vivo, and is applicable to development of stents for occlusive disease, TPEGs for aneurysmal disease, and other medical devices is highly desirable.
In designing a TPEG, several factors must be taken into account, such as the structural integrity of the TPEG, the prevention of perigraft leaks, the need for a more easily-controlled TPEG deployment to allow a more precise positioning of the TPEG, the kink resistance of the TPEG, the morphology of the arterial walls, the relatively large size and lack of TPEG flexibility in the undeployed configuration (which can create difficulties in passing the TPEG from its insertion site to its deployment site), and the like. In vivo boundary conditions and forces, particularly dynamic or static cyclic in vivo forces, and the material properties of a TPEG are also important factors. Taking these factors into consideration during virtual testing and development of a medical device generates a more accurate assessment of the maximum stresses, strains, and deformations, over time that may potentially be handled by a medical device such as a TPEG.
In designing a stent, several factors must be considered including radial force, crush resistance, flexibility (in both the compressed and the deployed configurations), fatigue life, and tissue intrusion through open stent cells. A system that allows rapid evaluation of these and other characteristics of a stent design before hardware prototypes are constructed, thereby reducing the cost and time required for development and also expanding the designer's capability to explore more exotic designs and possibly discover new and more advantageous stent designs within a given budget and timeframe is highly desirable.
Thus, systems and methods which allow accurate virtual testing of a medical device design with respect to one or more of the above noted factors, in addition to other factors not specifically enumerated, without the need for an actual prototype of the design, are needed. Such systems and methods can reduce the cost of medical device development and increase the safety and efficacy of the designs.